This proposal concerns an electrocardiographic method for sizing infarcted tissue and estimating size and severity of abnormalities of recovery in ischemic tissue. The electrocardiographic parameter proposed is the QRST isoarea map which is largely independent of activation sequence. Isoarea maps will be constructed from electrocardiograms recorded simultaneously from 192 leads or 32 optimally selected leads from which the entire thoracic potential distribution will be predicted. The method will be tested in dogs and humans. In dogs thermal and chemical lesions of controlled size will be investigated in addition to ischemic lesions. Videometry will also be employed to estimate infarct size in both the animal experiments and patient studies. The QRST isoarea map should provide useful information concerning anatomic infarct size. In addition, a derived map based on the QRS area and fractions of the T area from plus 1 to minus 1 should provide estimates of functional size and severity of ischemic lesions in terms of arrhythmia vulnerability.